I use valbazen often. It is the safest wormer on the market. Valbazen kills all known types of worms that chickens can get. It slowly kills worms over several days preventing toxic dead worm overload that other wormers cant. Dosage for standard size birds is 1/2cc given orally undiluted, 1/4cc for smaller birds. Repeat dosing in 10 days unless dealing with tapeworms.

I noticed your ID is jgcalifornia, but I don't know if that's because you have Jersey Giants or if it stands for something else, but if you do have them, the dose would be substantially higher for a JG rooster (13 pounds) and moderately higher for a hen (10 pounds).

If you want to calculate the dose based on 20mg/kg the formula is:

Weight of bird in pounds divided by 2.2 (that converts pounds to kg) times 20mg divided by 113.6

So for a 13 pound bird it would look like this:
13 / 2.2 x 20 / 113.6 = 1.04ml

Some people might say that I'm a little OCD when it comes to weighing and dosing, lol, but sometimes I dose chicks as small as 30 grams (not with wormer, but other meds), 300 gram bantams, 1000 gram bantams, 3kg fowl, 6kg fowl or turkeys as big as 30kg.

Your Faverolle and Cochins are good examples, both can be quite a bit bigger than the average chicken and would require more of most medications for the best efficacy. My Cochins are small, so for them 0.5ml (56.8mg) would be fine.

Disclaimer: I have not used Valbazen, but when I buy it, 20mg/kg is the amount I will use.